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Sedative and hypnotics Alcohols
Pharmacology Series By Dr. Ankit Kumar
Overview
This video explains the pharmacology of alcohols, focusing on ethanol, methanol, and ethylene glycol. It details their metabolism in the liver, the toxic byproducts formed, and the treatment strategies for poisoning. The video also delves into the complexities of ethanol addiction, including its mechanisms, withdrawal symptoms, and a multi-stage approach to treatment involving acute withdrawal management, prevention of future withdrawal, and relapse prevention using specific medications. Finally, it touches upon drugs that can cause disulfiram-like reactions.
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Chapters
- Alcohols (ethanol, methanol, ethylene glycol) are metabolized in the liver by alcohol dehydrogenase.
- This enzyme converts alcohols into toxic aldehydes: ethanol to acetaldehyde, methanol to formaldehyde, and ethylene glycol to glycol aldehyde.
- A second enzyme, aldehyde dehydrogenase, converts these aldehydes into acids: acetic acid, formic acid, and glycolic/oxalic acid, respectively.
- Formic acid (from methanol) is highly toxic to neurons and the retina, causing blindness and potential Parkinsonism. Glycolic acid is also neurotoxic, and oxalic acid can form kidney stones.
Understanding how different alcohols are metabolized into toxic substances is crucial for diagnosing and treating poisoning, as the specific toxic byproducts dictate the symptoms and treatment approach.
Methanol poisoning leads to blindness because the formic acid produced damages the retina.
- Fomepizole inhibits alcohol dehydrogenase, preventing the formation of toxic aldehydes from methanol and ethylene glycol.
- Disulfiram inhibits aldehyde dehydrogenase, preventing the conversion of acetaldehyde to acetic acid, and is used to deter ethanol consumption.
- Ethanol can also be used as a competitive inhibitor of alcohol dehydrogenase in methanol or ethylene glycol poisoning, saturating the enzyme to prevent toxic metabolite formation.
Specific drugs can either block the toxic metabolic pathway or be used therapeutically to manage addiction, highlighting the targeted nature of pharmacological interventions.
Fomepizole is the drug of choice for methanol poisoning because it stops the production of toxic formic acid.
- The treatment for methanol and ethylene glycol poisoning follows the 'SHAFE' mnemonic (or similar variations).
- Sodium bicarbonate is given to correct metabolic acidosis.
- Hemodialysis is a primary treatment to remove the toxic substances from the blood, especially if methanol levels are high.
- Antidotes like fomepizole are crucial, and ethanol can be used as a backup.
- Folinic acid (for methanol) helps convert toxic formic acid into less harmful CO2.
This structured approach ensures that all critical aspects of poisoning management—acidosis correction, toxin removal, and antidote administration—are addressed systematically.
Hemodialysis is mandatory if the blood methanol level exceeds 20 mg/dL.
- Ethanol is the second most abused substance after tobacco and leads to addiction characterized by pleasure, tolerance, and dependence.
- Tolerance means the body requires more alcohol to achieve the same effect.
- Dependence leads to dangerous withdrawal symptoms when alcohol intake stops.
- Acute withdrawal management focuses on treating symptoms like delirium tremens and seizures with benzodiazepines (e.g., IV diazepam, or lorazepam/oxazepam in liver failure).
- Vitamin B1 (thiamine) is given to prevent Wernicke-Korsakoff syndrome, and beta-blockers may be used for anxiety and tachycardia.
Recognizing the hallmarks of addiction and understanding how to manage the immediate, potentially life-threatening withdrawal symptoms is the first step in helping an individual overcome dependence.
Intravenous diazepam is the drug of choice for managing acute ethanol withdrawal symptoms like seizures, unless the patient has liver failure, in which case lorazepam or oxazepam is preferred.
- After stabilizing acute withdrawal, long-acting benzodiazepines like chlordiazepoxide are gradually tapered to prevent future withdrawal symptoms.
- To prevent relapse, medications are used to reduce craving (naltrexone, ondansetron, topiramate, acamprosate) or act as deterrents (disulfiram).
- Naltrexone and acamprosate are approved combination therapies for relapse prevention.
- Disulfiram acts as a deterrent by causing unpleasant physical reactions (disulfiram-like reaction) if alcohol is consumed, thus discouraging drinking.
- Disulfiram is contraindicated in active drinkers due to severe side effects and is only for maintaining abstinence.
A comprehensive addiction treatment plan extends beyond immediate withdrawal to include long-term strategies that address the psychological and physiological drivers of continued substance use.
Disulfiram is given to patients who have stopped drinking to create a strong aversion to alcohol by causing flushing, hypotension, and chest pain if they relapse.
- Certain drugs, besides disulfiram, can inhibit aldehyde dehydrogenase, leading to acetaldehyde accumulation and disulfiram-like reactions.
- These drugs should be avoided in active alcoholics.
- Common examples include metronidazole, griseofulvin, procarbazine, chlorpropamide, and certain cephalosporins.
Awareness of drugs that cause disulfiram-like reactions is critical for patient safety, preventing accidental severe adverse events in individuals who may be consuming alcohol.
Taking metronidazole while drinking alcohol can cause a severe reaction with flushing, nausea, and vomiting due to acetaldehyde buildup.
Key takeaways
- Alcohols are metabolized in the liver via dehydrogenase enzymes, producing toxic intermediates that cause specific poisoning syndromes.
- Fomepizole and ethanol serve as crucial antidotes by inhibiting alcohol dehydrogenase, thereby preventing the formation of toxic metabolites from methanol and ethylene glycol.
- Hemodialysis is a vital intervention for severe methanol and ethylene glycol poisoning, effectively removing toxins from the bloodstream.
- Ethanol addiction is a complex disease involving pleasure, tolerance, and dependence, requiring a multi-faceted treatment approach.
- Managing ethanol addiction involves treating acute withdrawal, preventing future withdrawal episodes with medications like benzodiazepines, and implementing relapse prevention strategies.
- Disulfiram deters alcohol consumption by inducing severe adverse reactions upon alcohol intake, but it is only suitable for patients who have already abstained.
- Several common medications can mimic disulfiram's effects, necessitating caution regarding alcohol consumption during their use.
Key terms
EthanolMethanolEthylene GlycolAlcohol DehydrogenaseAldehyde DehydrogenaseFormic AcidAcetaldehydeFomepizoleDisulfiramHemodialysisMetabolic AcidosisDelirium TremensBenzodiazepinesToleranceDependenceWithdrawal SymptomsRelapse PreventionDisulfiram-like Reaction
Test your understanding
- How does the metabolism of methanol lead to its characteristic toxicity, particularly blindness?
- What is the primary mechanism of action for fomepizole in treating methanol poisoning, and why is it preferred over ethanol in some cases?
- Describe the three main stages of managing ethanol addiction, including the types of medications used at each stage.
- Why is disulfiram considered a deterrent drug for alcohol addiction, and in which patient population is it absolutely contraindicated?
- What are disulfiram-like reactions, and what are three common classes of drugs that can cause them?